The present invention relates to novel powder coating suspensions (powder slurries) and powder coating materials preparable by an emulsification process. The present invention also relates to a process for preparing novel powder coating suspensions (powder slurries) and powder coating materials by emulsification. The present invention additionally relates to the use of the novel powder coating suspensions (powder slurries) and powder coating materials as coating materials, adhesives, and sealing compounds for coating, bonding, and sealing motor vehicle bodies and parts thereof, the interior and exterior of motor vehicles, the inside and outside of buildings, and doors, windows, and furniture, and for coating, bonding, and sealing in the context of the industrial coating particularly of small parts, coils, containers, packaging, electrical components, and white goods.
Powder coating materials in the form of aqueous suspensions which are substantially free from organic solvents and may be processed using liquid coating technologies, and processes for preparing them by melt emulsification, are known from the German patent application DE 196 52 813 A1. In this known process, the binders, the crosslinking agents, and any further additives are fed in the form of viscous resin melts into the dispersing equipment, in which they are dispersed finely in the liquid phase. Alternatively, before their dispersing in the dispersing equipment in the liquid state, the ingredients may first of all be mixed homogeneously with one another and then, in a second step, dispersed finely in the liquid phase. Thereafter, the resulting emulsion is converted by cooling into a suspension containing solid, finely divided particles. The key advantage of this process is that there is no need for complicated grinding processes, which under certain circumstances may damage the dispersions, in order to adjust the particles to the required size. Moreover, finer power coating suspensions can be produced by means of melt emulsification than by the grinding processes.
The German patent application does not disclose the isolation of the dispersed or suspended powder coating particles.
According to column 7 lines 4 to 9 of DE 196 52 813 A1, use may be made as stabilizers, dispersants or emulsifiers of short-chain amphiphilic polyacrylates prepared from acrylic acid, ethylhexyl acrylate, hydroxyethyl acrylate and an anionic comonomer in lyotropic phase by means of transfer polymerization. The surface tension of aqueous solutions of the emulsifiers at the critical micelle concentration (CMC), however, is not specified.
Powder slurries prepared by melt emulsification are also described in the German patent applications DE 100 06 673.9 and DE 100 18 581.9, unpublished at the priority date of the present specification. The resulting dispersed powder coating particles, however, are not isolated and used as powder coating materials. Emulsifiers used include nonionic emulsifiers such as alkoxylated alkanols and polyols, phenols and alkylphenols, or anionic emulsifiers such as alkali metal salts or ammonium salts of alkanecarboxylic acids, alkanesulfonic acids, and sulfo acids of alkoxylated alkanols and polyols, phenols and alkylphenols. The surface tension of aqueous solutions of the emulsifiers at the critical micelle concentration (CMC), however, is not specified.
Processes for preparing powder slurries and powder coating materials by melt emulsification are known from the international patent application WO 97/45476. According to page 13 lines 5 to 20 of the international patent application, emulsifiers are used in the process. In the case of an aqueous phase, polyethylene glycol or polyvinyl alcohol is used. The key factor is that the emulsifiers have an anchor component which links the emulsifiers to the melt by means of physical adsorption or chemical reaction. Examples of suitable anchor components are polar (meth)acrylate copolymers or the corresponding groups. The surface tension of aqueous solutions of the emulsifiers at the critical micelle concentration (CMC), however, is not specified.
Processes for preparing powder slurries and powder coating materials by melt emulsification are known from the international patent application WO 98/45356. Ionic and nonionic emulsifiers (surfactants) are used. Ionic emulsifiers used include the in situ reaction products of the carboxyl-containing olefin copolymers used in the process with ammonium hydroxide, triethanolamine, morpholine, and dimethylethanolamine. Preferred nonionic emulsifiers are alkylphenol thioxylates and ethylene oxide-propylene glycol copolymers. The surface tension of aqueous solutions of the emulsifiers at the critical micelle concentration (CMC), however, is not specified.
The processes known to date for preparing powder slurries and powder coating materials by melt emulsification have the disadvantage that the stabilizers, dispersants or emulsifiers employed are only able to effect adequate stabilization of either the emulsified melted particles formed to start with or the suspended solid particles which result after cooling of the emulsion, but not both simultaneously. With the known processes, therefore, there is a risk that they will react adversely even to slight variations in the process conditions and will not produce powder slurries and powder coating materials that meet the specification.
The use of dispersions of copolymers preparable in aqueous media by single-stage or multistage free-radical copolymerization of    a) at least one olefinically unsaturated monomer and    b) at least one olefinically unsaturated monomer different than the olefinically unsaturated monomer (a) and of the general formula IR1R2C═CR3R4   (I)            in which the radicals R1, R2, R3, and R4 each independently of one another are hydrogen atoms or substituted or unsubstituted alkyl, cycloalkyl, alkylcycloalkyl, cycloalkylalkyl, aryl, alkylaryl, cycloalkylaryl, arylalkyl or arylcycloalkyl radicals with the proviso that at least two of the variables R1, R2, R3 and R4 are substituted or unsubstituted aryl, arylalkyl or arylcycloalkyl radicals, especially substituted or unsubstituted aryl radicals,as binders in coating materials, especially aqueous basecoat materials (cf. the German patent application DE 199 30 665 A1), primer-surfacers and antistonechip primers (cf. the German patent application DE 199 30 067 A1), and clearcoat materials (cf. the German patent application DE 199 30 664 A1) is known. Their use as stabilizers, emulsifiers or dispersants is not described in the patent applications.        
It is an object of the present invention to find novel powder coating suspensions (powder slurries) and powder coating materials preparable by an emulsification process simply, reliably and reproducibly and meeting given specifications.